The disclosure relates to a manufacturing method of a liquid crystal display (LCD) device and, in particular, to a method for alignment treatment of a substrate for the LCD device.
In the manufacturing process of a LCD device, two substrates are combined by a sealing material, and a liquid crystal (LC) material is injected into the space between the two substrates. Then, polarizing films are attached to the outer surfaces of the substrates, respectively, and a printed circuit board (PCB) with driving circuits is installed. Finally, a backlight unit is added so as to form the LCD device.
The substrate of the LCD device is disposed with an alignment film, so that the liquid crystal (LC) molecules disposed between the two substrates can be homogenously aligned. The steps for forming the alignment film include: coating a polyimide (PI) layer, pre-baking the PI layer, heating to remove the solvent in the PI layer, baking the PI layer to form the polymer material by acetylation, and aligning the PI layer. The conventional methods for aligning the PI layer include the rubbing method and the photo alignment method (hereinafter photo align method). The rubbing method is to rub the alignment film with rayon, and the photo align method is to use the linear polarized UV (LPUV) light to irradiate the alignment film. However, the rubbing method usually causes some residual particles, so a cleaning apparatus is subsequently needed to clean the alignment film. This increases the manufacturing steps and cost. In addition, the rubbing process may produce unexpected blemishes such as dents or scrapes, which decrease the product yield. Moreover, the static electricity induced by the rubbing process may damage circuits which are disposed on the substrates.
In the conventional photo align method, a UV light with a specific polarized direction (e.g. a direction having an included angle of 45° with y axis) is used to irradiate the alignment film, so that the alignment film can perform a photo chemical reaction with directional selectivity (the photo chemical reaction only occurs on those related to y axis). Thus, the molecules of the alignment film can be aligned in a specific direction, so the curing ratio of the molecules of the alignment film must be less than or equal to 50%. The area of the alignment film, which is irradiated by the UV light with the specific polarized direction, has decreased absorptivity of UV light (such as 45° and 135° as shown in FIG. 6). In FIG. 6, the vertical axis represents the absorptivity of the alignment film, and the horizontal axis represents the included angle between y axis and the polarization direction of the LPUV light irradiating the alignment film.
With the conventional photo align technology, if it is desired that the alignment film have a plurality of alignment directions, a mask is needed to expose the alignment film in different directions. This process is therefore very complex.